Traditionally, diesel engines are used as a drive source of vessels such as tankers or transport ships and onshore power generation facilities. However, the exhaust gas of the diesel engine contains a large amount of nitrogen oxide, sulfur oxides, particulate matter, and the like which are harmful substances hindering preservation of the environment. For this reason, in recent years, gas engines that can reduce the amount of harmful substances generated are becoming prevalent as an alternative engine for diesel engines.
A so-called gas engine that generates power by using a fuel gas such as natural gas supplies a mixed gas obtained by mixing a fuel gas with the air to a cylinder and combusts the same (see Patent Literature 1; hereinafter PTL 1). Further, as an engine device combining the characteristics of a diesel engine and characteristics of a gas engine, there is a dual-fuel engine which allows a use of a premix combustion mode in which a mixture of a gaseous fuel (fuel gas) such as natural gas and air is supplied to a combustion chamber and combusted, in combination with a diffusion combustion mode in which a liquid fuel such as crude oil is injected into the combustion chamber and combusted (see patent Literature 2; hereinafter, PTL 2).